1. Field of the Invention
This invention relates to a network comprising a plurality of station units connected by a ring-like data transmission line enabling circular transmission of communication data in digital form in a single direction and, in particular to an abnormality recovery system in a network capable of maintaining a data transmission function in the network even if communication means being provided for each station unit for governing reception and transmission of communication data falls into an abnormal condition.
2. Description of the Related Art
Hitherto, a network generally has been known which comprises a plurality of station units connected by a ring-like data transmission line enabling circular transmission of communication data in digital form in a single direction.
To exchange communication data between station units in a network configured as described above, first a communication IC for governing reception and transmission of communication data is provided for each station unit and the communication data is sent from the communication IC in the station unit of the transmitting party in a predetermined direction on a data transmission line. The communication IC in the station unit downstream from the transmitting party on the data transmission line determines whether or not the home station unit is specified as the receiving party. If the home station unit is not specified as the receiving party, the communication IC sends the communication data to the station unit downstream from the home station unit. On the other hand, if the home station unit is specified as the receiving party, the communication IC reads the communication data over the data transmission line, thereby exchanging the communication data between the station units.
However, according to the conventional network as described above, if an abnormal condition such as a failure occurs in the communication IC in a station unit at a midpoint position on the route between the transmitting party and the receiving party, the communication data cannot be transmitted to station units downstream from the station unit falling into the abnormal condition. Resultantly, a problem of impairing the data transmission function in the network, to be solved is involved.